report work

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CHAPTER 1
INTRODUCTION
1.1 General introduction:
Ready Mix Concrete (RMC) is a specialized material in which the cement aggregates
and other ingredients are weigh-batched at a plant in a central mixer or truck mixer, before
delivery to the construction site in a condition ready for placing by the builder. Thus, `fresh'
concrete is manufactured in a plant away from the construction site and transported within the
requisite journey time. The RMC supplier provides two services, firstly one of processing the
materials for making fresh concrete and secondly, of transporting a product within a short time.
It is delivered to the worksite, often in transit mixers capable of mixing the ingredients
of the concrete just before the delivery of batch. This results in a precise mixture, allowing
specialty concrete mixtures to be developed and implemented on construction sites. The second
option available is to mix the concrete at the batching plant and deliver the mixed concrete to
the site in an agitator truck, which keeps the mixed concrete in correct form.
In the case of the centrally mixed type, the drum carrying the concrete revolves slowly
so as to prevent the mixed concrete from "segregation" and prevent its stiffening due to initial
set. However, in the case of the truck-mixed concrete, the batched materials (sand, gravel and
cement) are carried and water is added just at the time of mixing. In this case the cement
remains in contact with the wet or moist material and this phase cannot exceed the permissible
period, which is normally 90 minutes.
The use of the RMC is facilitated through a truck-mounted 'boom placer' that can pump
the product for ready use at multi-storied construction sites. A boom placer can pump the
concrete up 80 meters.
RMC is preferred to on-site concrete mixing because of the precision of the mixture and
reduced worksite confusion. It facilitates speedy construction through programmed delivery at
site and mechanized operation with consequent economy. It also decreases labour, site
supervising cost and project time, resulting in savings. Proper control and economy in use of
raw material results in saving of natural resources. It assures consistent quality through accurate
computerized control of aggregates and water as per mix designs. It minimizes cement wastage
due to bulk handling and there is no dust problem and therefore, pollution-free.
Ready mix concrete is usually ordered in units of cubic yards or meters. It must remain
in motion until it is ready to be poured, or the cement may begin to solidify. The ready mix
concrete is generally released from the hopper in a relatively steady stream through a trough
system. Workers use shovels and hoes to push the concrete into place. Some projects may
require more than one production run of ready mix concrete, so more trucks may arrive as
needed or additional batches may be produced offsite and delivered.
However there are some disadvantages of RMC to, like double handling, which results
in additional cost and losses in weight, requirement of go downs for storage of cement and
large area at site for storage of raw materials. Aggregates get mixed and impurities creep in
because of wind, weather and mishandling at site. Improper mixing at site, as there is

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ineffective control and intangible cost associated with unorganized preparation at site are other
drawbacks of RMC. There are always possibilities of manipulation; manual error and mischief
as concreting are done at the mercy of gangs, who manipulate the concrete mixes and water
cement ratio.
1.2 OBJECTIVE:
The main objective to choose this topic is that an engineer should have the knowledge
of advantages of RMC and disadvantages of Site mixed concrete. As RMC is being widely
used in bigger and medium size of projects today, Engineer should be aware of the technicality
of the RMC and the operational work, to ensure the quality of work and the Site Engineer
should know what are the steps to be taken to check the concrete in RMC, what is required to
be specified for RMC, what is the information required to be supplied by the RMC supplier,
what checks are necessary by the consumer before ordering RMC, what are the checks needed
at site prior and after to receipt of RMC.
1.3 NECESSITY:
Normally the concrete operation carried out in India, is of site mixed, which is having
some disadvantages which are shown below:
 Quality Assurance not guaranteed.
 Constant control on aggregates for size, shape & grading not exercised on site.
 Arbitrary batching and mixing by volume. Strict water-cement ratio not exercised.
 Wastage of materials.
 Retarded speed.
 Concreting operations prolonged beyond day light without proper lighting.
 Manual operation.
 Speed restricted depending on mixers.
 Restricted spaces.
 Storages of aggregates and cement.
 Blocking of roads / approaches
 Dust pollution
RMC is the perfect solution for the above disadvantages and offers the following advantages
by its usage, which makes it necessary as a part of the construction:
 Generally speaking, the quality of concrete will be superior than site mixed concrete.
However, it will greatly depend on the controls and checks exercised at site and at RMC
producer's plant.
 There is a considerable wastage of materials on site due to poor storage conditions and
repeated shifting of the mixer location. This is prevented if RMC is used.
 In most cities, the plot area is barely sufficient to store reinforcement steel, formwork,
concrete and other construction materials. Using RMC can cause less congestion and
better housekeeping on the site resulting in efficient working environment.

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 Obtaining RMC at site can reduce supervision and labour costs which would otherwise
be required for batching and mixing of concrete at site.
 Many sites in cities, house their work force on the site itself to reduce the time and cost
of daily travel. This creates unsafe and unhygienic conditions on the site as well as for
the surrounding areas. This will reduce to a certain extent if RMC is utilized.
 Fluctuation of raw material prices and their availability has always caused delays and
problems of inventory and storage for site producers of concrete. This is totally avoided
when RMC is used.
 Availability of labour gangs intermittently has always posed problems to concrete
producers on site. This can now be avoided. Besides these labour gangs are difficult to
supervise and control as they are only interested in completing the concreting
operations as fast as possible. This results in addition of excess water and inadequacies
in batching/mixing.
 A problem of inspection, checking and testing of all concrete materials on site is
avoided. However, to a certain extent these checks and tests may be required to be done
at RMC producers' plant.
 Concrete mix design and its control due to variations of material properties is avoided
as RMC producers are responsible for the same and supply concrete as specified by the
purchaser as per the requirements of the construction site.
 In public places it creates fewer nuisances. Congested roads and footpaths are often
blocked by carelessly stored concrete materials. RMC allows a much better flow of road
traffic as well as pedestrian movement.
 It improves the environment and around the site. Nuisance due to stone dust and cement
particles is reduced considerably. To a certain extent even noise pollution is reduced.
 The modern RMC plants have an automatic arrangement to measure surface moisture
on aggregates this greatly helps in controlling the water to cement ratio (w/c) which
results in correct strength and durability.
 RMC plants have proper facilities to store and accurately batch concrete admixtures
(chemical and mineral). To improve properties of concrete both in plastic and in
hardened stage this accuracy is useful.
 In general, RMC plants have superior and accurate batching arrangements than the
weigh batchers used on site.
 RMC plants have superior mixers than the rotating drum mixers generally used for
mixing concrete materials at site.
 RMC plants have efficient batching and mixing, facilities which improve both quality
and speed of concrete production.
 Temperature control of concrete in extreme weather conditions can be exercised in a
much better manner than done at site.

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 RMC helps encourage" mechanization and new technologies like pumped concrete bulk
transportation of cement production of self-compacting concrete and high strength high
performance concrete.
 New materials like micro silica and fibers can be safely used in RMC which in
conventional concrete may pose problems.
 Introduction of RMC improves the rate of supply of concrete in the formwork and
thereby automatically improves quality of formwork, layout of reinforcement steel and
its detailing and safety / strength of scaffolding and staging.
1.4 HISTORY:
The Idea of Ready Mix Concrete (RMC) was first introduced by Architect Jurgen
Heinrich Magens, he got his patent of RMC in Germany in 1903. In 1907, he discovered that
the available time for transportation could be prolonged not only by cooling fresh concrete but
also by vibrating it during transportation. So this gave rise to a concrete which is made in the
off site.
The first concrete mixed off site and delivered to a construction site was effectively done
in Baltimore, United States in 1913, just before the First World War. The increasing availability
of special transport vehicles, supplied by the new and fast growing automobile industry, played
a positive role in the development of RMC industry.
The first concept of transit mixer was also born in 1926 in the United States. In 1939,
the first RMC plant was installed in United Kingdom and in 1933, first specifications on RMC
was published in United Kingdom.
Between the years 1950 and 1980 considerable growth of RMC took place in the United
States with the maximum supply of 31 million cubic meters in the year 1974. However, on an
average RMC supplies were 25 million cubic meters per year between 1974 to 1980.
By 1990, in the United Sates there were 3700 RMC producers existing and 75% of
cement consumed by the construction industry was being utilized by RMC producers. In 1990
RMC plant in Japan were consuming nearly 70% of the total cement produced. In Malaysia,
RMC plants utilized nearly 16% of the total cement consumed in the year 1990. In UK, 43%
of the total cement consumed is being used by RMC plants.
RMC IN INDIA:
In India RMC was first initially was used in 1950 during the construction sites of Dams
like Bhakra Nangal, Koyna. At the construction the transportation of concrete is done by either
manually or mechanically using ropeways & buckets or conveyor systems.
RMC at Pune in the year 1991. However, due to various pit falls and problems this plant
did not survive for long and was closed. Within a couple of months in the year 1993, two RMC
plant were set up in Mumbai to commercially sell RMC to the projects where they were
installed. Unitech Construction set up one plant at Hiranandani Complex and Associated
Cement Companies set up another plant at Bharat Diamond Bourse Commercial Complex.

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These plants were later allowed to sell RMC to other projects also. Thus RMC was successfully
established sometime after 1994 in India.
RMC producers from outside India soon became interested in the Indian market and
therefore two very well-known producers set their foot on the Indian
soil i.e. Fletcher Challenge Ltd. From New Zealand and RMC Ready Mix of UK.
As per the available record up to 2003, there are around 76 RMC plant in 17 cities with
a total capacity of around 3875 cuM/hr, producing 3.8 million cuM of concrete per year.
Table1.4: Number of RMC plants and their capacities in leading metropolitan cities of
India.
Metro No. of plants Capacity (cu.m/hr)
Mumbai and Navy Mumbai 15 835
Bangalore 13 550
Delhi 11 660
Chennai 11 480
Hyderabad 7 350
1.5. SCOPE OF RMC IN INDIA:
Though delayed, but not very much, there a ready mixed concrete industry is
developing and expanding at a fast pace in the country on a large scale. Over the period, due
impetus to this development has been provided by various front-line construction and cement
companies as well as technological bodies. The World Bank's “ India Cement industry
Restructuring Project" under which a technical study report on the development of market for
bulk cement in India was made in 1996, proved to be positive development towards
modernization of cement distribution system in India, including setting up Ready mix concrete
Plants.
The objective of this technical study was to formulate an action plan for the
development of market for bulk cement in large cement centres in India and for gradual shift.
From the traditional mode of transportation in bags to bulk transportation through setting up of
ready mixed concrete plants in different parts of the country. The recommendation of the action
plan provided a useful guidance towards expanding bulk cement market thus paving a way for
installation or ready mixed concrete plants in India. According to Cement Manufacturers
Association, RMC is being increasingly recommended for all major public construction work
such as highways, flyovers. In cities like Bangalore and Chennai, even small house builders
have started displaying a marked preference for RMC instead of cement. According to the
experts, there is lot of scope for the development and growth of RMC in India. It can grow to

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consume 40-45 percent of cement by 2015 through setting up of RMC plants in various
consumption centres. For the healthy growth of industry, RMC industry in India has to fine-
tune its own practices to following practices elsewhere in the advanced countries where RMC
industry has been operating successfully. European Ready Mixed Concrete Organization
(ERMCO) has defined the broad objectives to be achieved in design, management and
operation of RMC which remain same as that of designing, and execution of concrete
construction projects. The marketing of RMC should no more be in terms of strength grades
only, but a combination of strength durability classification as per the Concrete Codes which
improves the sell ability of RMC in terms of the requirements of the projects. Appropriate
environmental, safety and health regulations for the working force need to be kept in mind in
the management and operation of RMC.

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CHAPTER 2
MATERIALS REQUIRED FOR RMC
2.1 AGGREGATE:
Aggregates are the important constituents in concrete. They give body to the concrete, reduce
shrinkage and effect economy. Earlier, aggregates were considered as chemically inert
materials but now it has been recognised that some of the aggregates are chemically active and
also that certain aggregates exhibit chemical bond at the interface of aggregate and paste. The
mere fact that the aggregates occupy 70-80 per cent of the volume of concrete, their impact on
various characteristics and properties of concrete is undoubtedly considerable. To know more
about the aggregates which constitute major volume in concrete.
Aggregates are divided into two categories from the consideration of size
 Coarse aggregate
 Fine aggregate
The size of the aggregate bigger than 4.75 mm is considered as coarse aggregate and aggregate
whose size is 4.75 mm and less is considered as fine aggregate.

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SAMPLING PROCEDURE FOR AGGREGATES USED IN CONCRETE:
All aggregates are to be sampled properly before taking them for testing. The purpose
of sampling is to get representative material for testing the wrong sampling of aggregate may
lead to any of the following:
 Consuming of bad quality of aggregates in concrete by accepting the bad quality of
materials at site.
 Disputing with the suppliers.
There is a definite procedure for sampling of aggregates. The procedure is explained
below:
 Collect the aggregate sample from different locations at different depths from the site
immediately after unloading the aggregates from the trucks. Collect the samples at least
from 10 to 15 locations.
 Thoroughly remix the sample collected from various places & depths of the trucks or
from the stocks.
 Make a cone from the sample.
 Flatten the cone sample to form a circle of uniform thickness.
 Divide the cone in to four equal quarters.
 Discard any two diagonally opposite segment of quartered sample.
 Collect the remaining sample & remix.
 Take this remixed aggregate for testing.
The material so sampled only should be taken for testing. The Indian standards recommend to
sample the aggregates as above. However it recommends collecting samples from different sub
lots which are not practical as it takes long time to build up the lots at site. Hence the method
suggested above may be conveniently adopted at site.
2.2 CEMENT:
Cement is a binder material which sets and hardens independently, and can bind other
materials together. Cement is made up of four main compounds tricalcium silicate (3CaO
SiO2), dicalcium Silicate (2CaO SiO2), tricalcium acuminate (3CaO Al2O3), and tetra-
calcium aluminoferrite (4caco Al2O3 Fe2O3).tetra-calcium aluminoferrite (4CaO Al2O3
Fe2O3). In an abbreviated notation differing from the normal atomic symbols, these
compounds are designated as C3S, C2S, C3A, and C4AF, where C stands for calcium oxide
(lime), S for silica and A for alumina, and F for iron oxide. Small amounts of uncombined lime
and magnesia also are present, along with alkalis and minor amounts of other elements.

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2.3 ADMIXTURE:
A substance added to the basic concrete mixture to alter one or more properties of the
concrete; i.e. fibrous materials for reinforcing, water repellent treatments, and colouring
compounds.
 Air-entraining admixtures (mainly used in concrete exposed to freezing and thawing
cycles).
 Water-reducing admixtures, plasticizers (reduce the dosage of water while maintaining
the workability).
 Retarding admixtures (mainly used in hot weather to retard the reaction of hydration).
 Accelerating admixtures (mainly used in cold weather to accelerate the reaction of
hydration).
 Super plasticizer or high range water-reducer (significantly reduce the dosage of water
while maintaining the workability)
 Miscellaneous admixtures such as corrosion inhibiting, shrinkage reducing, colouring,
pumping etc.

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Role of Admixture in Ready Mix Concrete:
The role of admixture is ready mixed of concrete is same as that in normal concrete.
However, admixture used in RMC is modified to meet the requirement of pumpable concrete
and other properties of concrete. The types of admixture used in RMC are generally termed as
Super plasticizers.
The history of admixture is as old as history of concrete. There are several types of
admixture available in market. But few admixtures namely Plasticizers and Super plasticizers
are of recent interest. These of admixture were initially developed in Japan and German around
1970. IN India use of admixture was recognized after 1985.In 1990 admixture started to gain
Importance after introducing Ready Mixed Concrete. The importance of admixture was further
recognized after revision on of IS: 456 - 1978. The earlier versions of IS 456 have permitted to
use w/c ratio as high as 0.65 in RCC works. The Revised IS 456-2000 has Restricted the w/c
ratio to 0.55 for mild exposure and 0.50 for moderate exposure ,0.45 for severe and very severe
exposure and 0.40 for extreme weathering conditions. The restriction on w/c ratio has made
the use of admixture all the more compulsory ingredient of concrete.
Admixture is used in RMC are of following types:
 Chemical admixture
 Mineral admixture
 Chemical and mineral admixture
In RMC admixture mainly perform the following functions:
 Increasing workability
 Accelerate or retard the setting time of concrete.
 Reduce segregation and bleeding in concrete.
 Improve pump ability.
2.4 FLY ASH:
Fly ash is a by-product from coal-fired electricity generating power plants. The coal
used in these power plants is mainly composed of combustible elements such as carbon,
hydrogen and oxygen (nitrogen and sulphur being minor elements), and non-combustible
impurities (10 to 40%) usually present in the form of clay, shale, quartz, feldspar and limestone.
As the coal travels through the high-temperature zone in the furnace, the combustible elements
of the coal are burnt off, whereas the mineral impurities of the coal fuse and chemically
recombine to produce various crystalline phases of the molten ash. The molten ash is entrained
in the flue gas and cools rapidly, when leaving the combustion zone (e.g. from 1500°C to 200°C
in few seconds), into spherical, glassy particles. Most of these particles fly out with the flue
gas stream and are therefore called fly ash. The fly ash is then collected in electrostatic
precipitators or bag houses and the fineness of the fly ash can be controlled by how and where
the particles are collected. Fly ash use improves concrete performance, making it stronger,

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more durable, and more resistant to chemical attack. Fly ash use also creates significant benefits
for our environment.
The size of fly ash ranges from 1.0 to 100 micron & the average size is around 20
microns. It is found that particle size below 10 microns contributes towards early Development
of strength (7& 28 days). The particle size of fly ash between l0 & 40 microns Contributes
towards the development of strength between 28 days & 1 year. The particle size above 45
microns does not contribute towards development of strength even after 1 year and for all
practical purpose they should be considered only as sand.
The fly ash is generally used in the concrete in the following ways.
 As partial replace for cement.
 As partial replacement for sand.
 As simultaneous replacement for both cement and sand.
It is found that fly ash replacement from l0 to 30% increases the development of Strength
up to 3 month or even more depending on the fineness of fly ash & its reaction with Calcium
hydroxide released during primary hydration of cement.
Addition of fly ash as per replacement of cement improves the workability of concrete
for the same water content. This means that the water content can be reduced for fly ash based
concrete. This reduced water cement ratio to some extent can offset for initial gain of Strength
can range from 10 to 25 % of the difference in strength between the strength of Normal concrete
& fly ash concrete.

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Fly ash as a partial replacement for sand is uneconomical and sometimes it is inevitable
in pumping concrete especially when coarser types of fine aggregates are used in concrete. It
is also found that partial replacement of fly ash marginally increases the strength Concrete due
to filler effect in the initial stages and due to pozzolanic action in 28days.Simultaneous use of
fly ash as a partial replacement of cement and sand is good Proposal to increase strength,
workability & pump ability of concrete.
2.5 WATER:
The pH value of water should be in between 6.0 and 8.0 according to IS 456-2000.
Effect of Mixing Sea Water in Concrete:
The sea Water generally contains salinity of about 3.5% in which about 80% is sodium
chloride. Many researchers have been conducted to study the corrosion problem of steel
Embedded in concrete where sea water is used as mixing water in concrete nevertheless the
Indian standard is adamant & do not permit using sea water for mixing or curing in reinforced
Concrete constructions, but allows for using of sea water only for PCC work that too under
unavoidable circumstances.
Quality of Water for Curing Concrete Members:
Generally the water that is fit for mixing of water in concrete is also fit for curing.
However where appearance is important, water containing impurities which cause stains should
not to be used. The most important elements that cause stains in the concrete are iron, and
organic matters. It is also found that even sea water also causes stains in concrete. Hence water
containing iron, organic matters and also sea water should not be used for curing of concrete
when appearance is also set as criteria for the acceptance of concrete.
Quality of Water for Curing Concrete Cubes:
The water that is fit for mixing and curing of water for concrete is also fit for curing of
cubes which are cured under water. However the curing water should not to be allowed to
remain in stagnant condition in water tanks for long time. As a guideline the water tanks shall
be cleaned twice a week or when ph value of water reaches a value more than 9. The cleaned
Water tanks shall be refilled with fresh water every time.
The cleaning of water is necessary to remove algae and fungus materials developed
inside the water tanks which otherwise alters the setting and strength gaining properties of
Concrete. The low results of such cubes may call for in situ tests resulting in consequential
Delay of the project.

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CHAPTER 3
EQUIPMENTS REQUIRED
3.1 BATCHING PLANT:
The principal functional elements of every stationary concrete production Plant
comprises of the following:
 Storage of materials - Silos, containers and bins
 Batching arrangement
 Measuring and recording equipment
 Mixing equipment
 Control systems
 Electrical, hydraulic and pneumatic drives
 Conveying systems (belt / screw conveyors)

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3.1.1 Storage of Materials
i) Cement
Cement is generally stored in silos. The loading of cement is done with the help of
pneumatic blower systems either installed on bulk carriers or a separate system available at the
plant. If baggage cement is used then the cement is loaded using a compressed air loader and a
splitter unit. Cement is weighed separately, and is transported from the silo into a mechanical
or electro mechanical weigher by means of a screw conveyor.
ii) Water
Water is generally stored in tanks located close to the plant. It is accurately measured
by a water gauge and microprocessor controlled system. The modern plants have new litronic
MFM 85 moisture recorders. These recorders actually measure the moisture present in sand
while the entire batch flows past. A recording unit calculates the average moisture value of the
sand and passes on the information to the batching control unit to allow corrective action to be
taken. The system operates to an accuracy of as low as 0.2% relative moisture.
Consistency of the mix is generally checked by visual observation later confirming it
with a workability test like the slump test. However, in modern plants consistency of the
concrete mix is checked by a remote recording system which is automatic, easy and more
accurate.If concrete is very dry (stiff) the electrical resistance of the batch is measured and if
the concrete is wet the motor output is measured.
Accurate maintenance of the workability (consistency) of one cubic meter batch of
concrete may depend on as little as one litre or less of water. It is scarcely conceivable that
such a production process could be controlled without actually measuring the workability and
later correcting the consistency.
iii) Aggregates
The storage of aggregates is done in various way depending on the type of plant.
There are basically three types of plants generally in use.
 Vertical Production Plant
In this the aggregates are stored above the batching and mixing elements, in one or more
silos. These plants are not suitable for relocation at short intervals of time. As the aggregates
are stored in silos it is relatively easy to protect the aggregates from very low temperature in
winter period.
 Horizontal Production Plant
They can be again broadly classified into four types
i) Star pattern aggregate storage
ii) Storage in tall silo
iii) Storage in pocket silo
iv) Inline aggregate storage silos

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The star bin storage of aggregates is most popular in India mainly because of climate
conditions. The aggregates can be stored exposed to ambient temperature in different
compartments forming a star type pattern. A storage capacity of up to 1500 cuM is possible in
this type. The star pattern aggregates are stored in four to six compartments. They are bulked
at a 45 degree flow angle against the batching plant's bulkhead and partition wall of the
compartments using a boom type dragline loader. The drag-line operations are either fully
manual, semi-automatic or fully automatic. Fully automatic dragline loader system operator.
The star bin type plant requires more space and as the aggregates are stored in open
they heat up at high ambient temperatures and freeze at very low temperatures. These types of
plants are not suitable in extreme weather conditions.
In silo type storage additional investment for loading equipment such as hopper, bucket
elevator or conveyor belt plus rotary distribution are required. They have large active storage
(up to 500 cuM) in a small areas. Loading is fully automatic, aggregates are well protected in
extreme climatic conditions and storage is very clean.
3.1.2 MIXING ARRANGEMENTS
There are various types of concrete mixers used on the concrete production plant. The two
basic types are free fall mixers and power mixers. Most of our indigenously manufactured
plants have free fall mixer. Free fall mixer consists of a rotating drum with blade fixed on the
drum's interior. As the drum rotates, the material inside is lifted and dropped. The drum is
loaded and emptied by changing the direction of rotation, dropping a flap or tipping it.
Most of the imported plants have power mixer. The power mixer sets in motion the
materials positively. The materials get thoroughly mixed by rotating arms. These mixers have
shorter mixing time; give better homogeneity, consistency and strength to the concrete.
Besides, they have better facility for inspection. The following are the most common designs.
Table 3.1: most common designs
If mixing is to be done on difficult concrete mixes, additional agitator is provided. The
pan type mixer with additional agitator or two agitators is claimed to be far in advance of any
Power
Mixer
Capacity CuM
(Compacted
concrete)
Output CuM/hr
(Compacted
concrete)
Max. Aggregate
size (mm)
Mixing Time (Sec)
30 15
Single
Shaft
3 120 --- 150
Twin Shaft 3.5 120-150 --- 190
Pan Type 3 120 --- 64

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if other mixer. Using additional agitators almost halves the mixing time. The additional agitator
is driven by a separate hydraulic system and can be set to any speed between 0 to 200
revolutions per minute.
3.1.3 CONTROL SYSTEMS
Almost all imported production plants offer automatic systems for control functions.
These are required for better quality control, higher economy and superior working conditions.
Fully automatic plant control systems with multiple inputs for up to 120 mixes or template
control system are usually housed in a container or control room of the plant. Microprocessor
controlled production plants represent the state of the art in the developed countries.
These controls are operated from main desk. It also has material availability monitor
and printer plus an additional batching monitor. The entire plant can be operated by just one
person. Microprocessor control besides having fully automatic running facility offers number
of additional features like statistical data recording and processing, a printer unit, moisture
adjustment arrangement, customer address, memory etc.
All you need to do is push the required mix template into the slot and press the "start"
button and the control system does the rest. Aggregate and cement weighment, moisture
correction, overrun correction and additive weighment are done accurately to give the concrete
mix of desired strength and workability.
The built in trouble shooting programs are most valuable and have a high reliability
factor. Even upto 1500 mixes of different types can be stored along with names and addresses
of the consumer and other data which is required to be stored in the computer for operation of
the plant. The mix data with quantity can be if required printed by the printer which is very
useful for invoicing the consumer for the concrete supplied to them.

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3.2 TRANSPORTATION EQUIPMENT: TRANSIT MIXER
There are developments taking place all over the world for different types of concrete
equipments. However, the transit mixer is one of the most .popular equipments out of several
modes available. In India too, a number of transit mixers are in use all over the country which
are mainly mounted on Indian truck chassis. The mixer drum is either manufactured in India
or is improved. However, in general, the hydraulic system is improved.
There are several types and capacities of transit mixers available as given below:
Table 3.2: capacities of transit mixers
Normal Capacity 4 to 12 CuM
Hydraulic Drive of Mixer Separate engine or driven by truck engine
Water tank capacity 192 to 2000 liters
Mixer trucks Twin axles for 4 CuM capacity
Three axles for 6 to 7 CuM capacity
Three/ four axles for 8 to 10 CuM capacity
Semi-trailer for 10 to 12 CuM.
In India 4 Cum. Truck mixers are popular while the 6 and 7 Cum. Truck mixers
mounted on a 3 axle chassis enjoy a leading position on all world markets as it has a favorable
cost- performance ratio, large selection of chassis, good maneuverability and is more suited to
general batch size requirements.

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CHAPTER 4
MIXING PROCESS
Thorough mixing of the materials is essential for the production of uniform concrete.
The mixing should ensure that the mass becomes homogeneous, uniform in colour and
consistency. There are three methods adopted for mixing Ready Mix Concrete.
Following are the three types of mixing process of RMC:
1. Transit Mixed (or "truck-mixed") Concrete
2. Shrink Mixed Concrete
3. Central Mixed Concrete
4.1 TRANSIT MIXED (OR "TRUCK-MIXED") CONCRETE
While ready mixed concrete can be delivered to the point of placement in a variety of
ways, the overwhelming majority of it is brought to the construction site in truck-mounted,
rotating drum mixers. Truck mixers have a revolving drum with the axis inclined to the
horizontal. Inside the shell of the mixer drum are a pair of blades or fins that wrap in a helical
(spiral) configuration from the head to the opening of the drum. This configuration enables the
concrete to mix when the drum spins in one direction and causes it to discharge when the
direction is reversed.
To load, or charge, raw materials from a transit mix plant or centrally mixed concrete
into the truck, the drum must be turned very fast in the charging direction. After the concrete
is loaded and mixed, it is normally hauled to the job site with the drum turning at a speed of
less than 2 rpm.
Since its inception in the mid-1920, the traditional truck-mixer has discharged concrete
at the rear of the truck. Front discharge units, however, are rapidly becoming more popular
with contractors. The driver of the front discharge truck can drive directly onto the site and can
mechanically control the positioning of the discharge chute without the help of contractor
personnel.
Currently, because of weight laws, the typical truck mixer is a 7 to 8.5 m3. The drums
are designed with a rated maximum capacity of 63% of the gross drum volume as a mixer and
80% of the drum volume as an agitator. Generally, ready mixed concrete producers, load their
trucks with a quantity at or near the rated mixer capacity. Fresh concrete is a perishable product
that may undergo slump loss depending on temperature, time to the delivery point on the job
site, and other factors.
Water should not to be added to the mix unless the slump is less than that which is
specified. If water is added, it should be added all at once and the drum of the truck mixer
should be turned minimum of 30 revolutions, or about two minutes, at mixing speed.
The ASTM C 94, Specification for Ready Mixed Concrete, indicates that the concrete
shall be discharged on the job site within 90 minutes and before 300 revolutions after water
was added to the cement. The purchaser may waive this requirement, when conditions permit.

19
In certain situations, air-entraining, water reducing, set-retarding or high-range water
reducing admixtures may need to be added to concrete prior to discharge to compensate for
loss of air, high temperatures or long delivery times. The ready mixed concrete producer will
assist the purchaser in such circumstances.
Fig.1 miller with transit mixed concrete

20
4.2SHRINK MIXED CONCRETE
Concrete that is partially mixed in a plant mixer and then discharged into the drum of
the truck mixer for completion of the mixing is called shrink mixed concrete. Central mixing
plants that include a stationary, plant-mounted mixer are often actually used to shrink mix, or
partially mix the concrete. The amount of mixing that is needed in the truck mixer varies in
these applications and should be determined via mixer uniformity tests. Generally, about thirty
turns in the truck drum, or about two minutes at mixing speed, is sufficient to completely mix
shrink-mixed concrete.
Fig .2 shrink mixed concrete in batching plant
4.3 CENTRAL MIXED CONCRETE
Central-mixing concrete batch plants include a stationary, plant-mounted mixer that
mixes the concrete before it is discharged into a truck mixer. Central-mix plants are
sometimes referred to as wet batch or pre-mix plants. The truck mixer is used primarily as an
agitating haul unit at a central mix operation. Dump trucks or other non-agitating units are
sometimes be used for low slump and mass concrete pours supplied by central mix plants.
About 20% of the concrete plants in the US use a central mixer. Principal advantages include:
 Faster production capability than a transit-mix plant
 Improved concrete quality control and consistency and
 Reduced wear on the truck mixer drums.

21
There are several types of plant mixers, including:
 Twin shaft mixer
 Tilt drum mixer
 Horizontal shaft paddle mixer
 Pan mixer
 Slurry mixer
Twin shaft mixer:
Twin-shaft mixers are ideal for the ready-mix and precast concrete industries where
large volumes of high quality concrete are demanded. The powerful twin-shaft mixer, with
counter rotating shafts, delivers fast mixing action and rapid discharge and handles mix designs
with coarse aggregates up to 6 inches in diameter. Generally most the RMC plants in India uses
Twin-shaft mixer.
The tilting drum mixer:
Tilting drum mixer is the most common American central mixing unit. Many central-
mix drums can accommodate up to 12 yd3 and can mix in excess of 200 yd3 per hour. They
are fast and efficient, but can be maintenance-intensive since they include several moving
parts that are subjected to a heavy load.
Horizontal shaft mixers:
Horizontal shaft mixers have a stationary shell and rotating central shaft with blades or
paddles. They have either one or two mixing shafts that impart significantly higher horsepower
in mixing than the typical drum mixer. The intensity of the mixing action is somewhat greater
than that of the tilt drum mixer. This high energy is reported to produce higher strength concrete
via to thoroughly blending the ingredients and more uniformly coating the aggregate particles
with cement paste. Because of the horsepower required to mix and the short mixing cycle
required to complete mixing, many of these mixers are 4 or 5 yd3 units and two batches may
be needed to load a standard truck or agitator.
Pan mixers:
Pan mixers are generally lower capacity mixers at about 4 to 5 yd3 and are used at
precast concrete plants.
Slurry Mixing:
The slurry mixer is a relative newcomer to concrete mixing technology. It can be added
onto a dry-batch plant and works by mixing cement and water that is then loaded as slurry into
a truck mixer along with the aggregates. It is reported to benefit from high energy mixing.
Another advantage is that the slurry mixer reduces the amount of cement dust that escapes into
the air.

22
CHAPTER 5
TESTS ON MATERIALS
5.0 INTRODUCTION:
All the ingredients used for preparation of the concrete, are thoroughly tested for their
quality and physical properties in a well-equipped laboratory attached to the plant for
conformity to relevant Indian Standard Codes. The moisture probe determines the water
content in the sand and aggregates. This accordingly helps in fixing the proportion of water to
be added for the preparation of the mix. The sand being used is passed through the mechanized
sieving system, before feeding for mixing.
Trial mixes are carried out and tested to ensure that each and every batch of concrete
coming out of the plant meets the parameters of client’s requirements. The sand being used is
passed through the mechanized sieving system, before feeding for mixing.
5.1 TESTS ON FINE AGGREGATE:
SEIVE ANALYSIS:
 A gradation test is performed on a sample of aggregate in a laboratory. A typical sieve
analysis involves a nested column of sieves with wire mesh cloth (screen).
 A representative weighed sample is poured into the top sieve which has the largest
screen openings. Each lower sieve in the column has smaller openings than the one
above. At the base is a round pan, called the receiver.
 The column is typically placed in a mechanical shaker. The shaker shakes the column,
usually for some fixed amount of time. After the shaking is complete the material on
each sieve is weighed. The weight of the sample of each sieve is then divided by the
total weight to give a percentage retained on each sieve.
 The size of the average particles on each sieve then being analysis to get the cut point
or specific size range captured on screen.
 The results of this test are used to describe the properties of the aggregate and to see if
it is appropriate for various civil engineering purposes such as selecting the appropriate
aggregate for concrete mixes and asphalt mixes as well as sizing of water production
well screens.
 The results of this test are provided in graphical form to identify the type of gradation
of the aggregate.
A suitable sieve size for the aggregate should be selected and placed in order of decreasing
size, from top to bottom, in a mechanical sieve shaker. A pan should be placed underneath the
nest of sieves to collect the aggregate that passes through the smallest. The entire nest is then
agitated, and the material whose diameter is smaller than the mesh opening pass through the
sieves. After the aggregate reaches the pan, the amount of material retained in each sieve is
then weighed.

23
Preparation:
In order to perform the test, a sample of the aggregate must be obtained from the source. To
prepare the sample, the aggregate should be mixed thoroughly and be reduced to a suitable size
for testing. The total weight of the sample is also required.
Reporting of results:
The results are presented in a graph of percent passing versus the sieve size. On the graph the
sieve size scale is logarithmic. To find the percent of aggregate passing through each sieve,
first find the percent retained in each sieve. To do so, the following equation is used,
%Retained = WSieve/WTotal × 100%.
Where WSieve is the weight of aggregate in the sieve and WTotal is the total weight of the
aggregate. The next step is to find the cumulative percent of aggregate retained in each sieve.
To do so, add up the total amount of aggregate that is retained in each sieve and the amount in
the previous sieves. The cumulative percent passing of the aggregate is found by subtracting
the percent retained from 100%.
%Cumulative Passing = 100% - %Cumulative Retained.
The values are then plotted on a graph with cumulative percent passing on the y axis and
logarithmic sieve size on the x axis.
METHODS
There are different methods for carrying out sieve analysis, depending on the material to be
measured.
Throw-action sieving
Here a throwing motion acts on the sample. The vertical throwing motion is overlaid
with a slight circular motion which results in distribution of the sample amount over the whole
sieving surface. The particles are accelerated in the vertical direction (are thrown upwards). In
the air they carry out free rotations and interact with the openings in the mesh of the sieve when
they fall back. If the particles are smaller than the openings, they pass through the sieve. If they
are larger, they are thrown upwards again. The rotating motion while suspended increases the
probability that the particles present a different orientation to the mesh when they fall back
again, and thus might eventually pass through the mesh.
Modern sieve shakers work with an electro-magnetic drive which moves a spring-mass
system and transfers the resulting oscillation to the sieve stack. Amplitude and sieving time are
set digitally and are continuously observed by an integrated control-unit. Therefore sieving
results are reproducible and precise (an important precondition for a significant analysis).
Adjustment of parameters like amplitude and sieving time serves to optimize the sieving for
different types of material. This method is the most common in the laboratory sector.
Horizontal sieving
In a horizontal sieve shaker the sieve stack moves in horizontal circles in a plane.
Horizontal sieve shakers are preferably used for needle-shaped, flat, long or fibrous samples,
as their horizontal orientation means that only a few disoriented particles enter the mesh and

24
the sieve is not blocked so quickly. The large sieving area enables the sieving of large amounts
of sample, for example as encountered in the particle-size analysis of construction materials
and aggregates.
Tapping sieving
 A horizontal circular motion overlies a vertical motion which is created by a tapping
impulse. These motional processes are characteristic of hand sieving and produce a
higher degree of sieving for denser particles (e.g. abrasives) than throw-action sieve
shakers.
EXPERIMENT RESULTS:
For Fine aggregate
Table 5.1: sieve analysis of fine aggregate test results
Sieve
size
Weight
(gm)
Retained
%
(col.2/W)
Cumulative
%
% of
Passing
(100 –
col.4)
Specification limits as
per Table-2 as per
IS383
1 2 3 4 5 Zone-
1
Zone-
2
Zone-
3
10.00mm 0 0 0 100 100 100 100
4.75mm 15.9 1.59 1.59 98.41 90-
100
90-100 90-100
2.36mm 128.4 12.84 14.43 85.57 60-95 75-100 85-100
1.18mm 102.5 10.25 24.68 75.32 30-70 55-90 75-100
0.600mm 321.3 32.13 56.81 43.19 15-34 35-59 60-79
0.300mm 213.5 21.35 78.16 21.84 5-20 8-30 12-40
0.150mm 91.2 9.12 87.28 12.72 0-10 for River sand & 0-
20 for Crusher sand
0.075mm 48.1 4.81 92.09 7.91 0-8 for River sand & 0-15
for Crusher sand
Result: From Table-2 of IS 383 the sample is from grading zone II.

25
SPECIFIC GRAVITY:
In Concrete technology, Specific gravity of aggregates is made use of in design
calculations of concrete mixes. With the specific gravity of each constituent known, its weight
can be converted into solid volume and hence a theoretical yield of concrete per unit volume
can be calculated.
Preparation of Test Sample
Fine Aggregate
a) Obtain a test sample of approximately 1100 grams from the material to be tested by one of
the following methods:
(1) Use of a sample splitter.
(2) Method of quartering after being thoroughly mixed and in a damp condition.
(3) By taking small scoops of material from various places over the field sample, after it has
been dampened and thoroughly mixed. In order to avoid segregation, the material must be
damp enough to stand in a vertical face when cut with a trowel. This method of sample
reduction is applicable to sands only.
b. If the material has been continuously wet before being received on the job, it may be assumed
to be saturated. Otherwise, the sample must be saturated by immersing it in water for period of
not less than 15 hours.
c. After soaking, pour off the free water, spread the wet sample on a flat, nonabsorbent surface,
and allow it to come to a surface-dry condition by natural evaporation of free moisture.
Circulation of air by means of a fan may also be used to attain the surface-dry condition. The
sample should be stirred frequently to secure uniform drying.
Test Procedure
 Weigh the saturated-surface-dry sample to the nearest 0.5-gram. For ease in
calculations, the fine aggregate sample may be brought to exactly 1000 grams weight,
and the coarse aggregate sample may be brought to exactly 2000 grams weight.
 Place the sample in the appropriate pycnometer containing approximately two inches
of water.
 Nearly fill the pycnometer jar with water at the same temperature plus or minus 3°F
(1.7°C) as used in the calibration.
 Screw the cap down into the proper position by lining up the mark on the pycnometer
top and the jar.
 Entirely fill the pycnometer by adding additional water through the hole in the
pycnometer top.
 Hold one finger over the hole in the top and gently roll and shake the pycnometer to
remove any trapped air in the sample.
 When further rolling and shaking brings no more air bubbles to the top, fill, dry and
weigh as in step C3.

26
EXPERIMENT RESULTS:
For Fine aggregate
Table 5.2: specific gravity fine aggregate test results
Description Sample
1
Sample
2
Sample
3
A) Weight of the oven dry sample in air (gm) 490.2 484.5 487
B) Weight of the sample in water (gm) 301.5 300.5 303
C) Weight of the saturated surface dry sample (gm) 492 486.5 488
D) Specific gravity = A/(C-B) 2.573 2.604 2.632
E) Water absorption (%) = 100*(C-A)/A 0.367 0.412 0.205
Average specific gravity = 2.603
Average water absorption (%) = 0.328
BULK DENSITY TEST:
Objective:
Calculating the bulk density of fine aggregate samples.
Bulk Density:
When dealing with aggregates it is important to know the voids that presents between
the aggregate particles, so that we decide whether to fill them with finer aggregate or with
cement paste. We all know that the Density we often deal with equals the mass divided by the
volume, when using this law to measure the density of aggregates the volume we use is the
volume of aggregate + the volume of the voids, and in this case we get a new quantity called
the Bulk Density. Bulk Density = Mass of the aggregate Volume of aggregate particles with
voids between them. This bulk density is used to convert quantities by mass to quantities by
volume. Bulk density depends on several factors: Size distribution of aggregates, Shape of
particles and degree of compaction. There are two methods this quantity is measured by
 Loose method.
 Compaction method.
Apparatus and Materials:
1. Container.
2. Glass Plate.

27
3. Fine and Coarse aggregate sample.
4. Water
5. Weighting Machine.
Procedure:
It is the same procedures for fine and coarse aggregate samples.
1. Weighing the empty container with the glass plate.
2. Fill the container with coarse aggregate to over flowing and then using the plate to level the
surface, and the weight of the container and the plate and the coarse sample is found. (W1)
3. Empty the container from the coarse aggregate and refill it with the fine aggregate to over
flowing and then level the surface using the plate, and the weight of the container and the plate
and the fine sample is found. (W2)
4. Empty the container again and this time we fill it with water till the rim of it and place the
plate on it, no water bubbles should present on the surface, and we weight the container and
the plate and the water. (W3)
EXPERIMENT RESULTS:
Dry Loose Bulk Density of fine aggregate:
Weight of container = 2.540 Kg
Weight of total Sample in container = 4.580 Kg
Container Volume = 3 lit
Dry loose bulk density = 1526 gm / lit
Dry Compacted Bulk Density of fine aggregate:

28
AFTER ABSORPTION TEST:
This test helps to determine the water absorption of coarse aggregates as per IS: 2386
(Part III) – 1963. For this test a sample not less than 2000g should be used. The apparatus used
for this test are:
 Wire basket, perforated, electroplated or plastic coated with wire hangers for
suspending it from the balance.
 Water-tight container for suspending the basket.
 Dry soft absorbent cloth – 75cm x 45cm (2 nos.).
 Shallow tray of minimum 650 sq.cm area.
 Air-tight container of a capacity similar to the basket and Oven.
Procedure to determine water absorption of Aggregates:
i) The sample should be thoroughly washed to remove finer particles and dust, drained and
then placed in the wire basket and immersed in distilled water at a temperature between 22 and
32C.
ii) After immersion, the entrapped air should be removed by lifting the basket and allowing it
to drop 25 times in 25 seconds. The basket and sample should remain immersed for a period
of 24 + ½ hrs afterwards.
iii) The basket and aggregates should then be removed from the water, allowed to drain for a
few minutes, after which the aggregates should be gently emptied from the basket on to one of
the dry clothes and gently surface-dried with the cloth, transferring it to a second dry cloth
when the first would remove no further moisture. The aggregates should be spread on the
second cloth and exposed to the atmosphere away from direct sunlight till it appears to be
completely surface-dry. The aggregates should be weighed (Weight ‘A’).
iv) The aggregates should then be placed in an oven at a temperature of 100 to 110oC for 24hrs.
It should then be removed from the oven, cooled and weighed (Weight ‘B’).
Formula used is Water absorption = [(A - B)/B] x 100%.
Two such tests should be done and the individual and mean results should be reported.
EXPERIMENT RESULT:
Weight of Saturated Surface Dry (SSD) sample (A) =725.00 gm.
Weight of Oven dry Sample (B) =705.00 gm.
Weight Absorption =725-705/705 X 100
= 0.02837 X 100
= 2.83 %

29
5.2 TESTS ON COARSE AGGREGATES:
SEIVE ANALYSIS:
 A gradation test is performed on a sample of aggregate in a laboratory. A typical sieve
analysis involves a nested column of sieves with wire mesh cloth (screen).
 A representative weighed sample is poured into the top sieve which has the largest
screen openings. Each lower sieve in the column has smaller openings than the one
above. At the base is a round pan, called the receiver.
 The column is typically placed in a mechanical shaker. The shaker shakes the column,
usually for some fixed amount of time. After the shaking is complete the material on
each sieve is weighed. The weight of the sample of each sieve is then divided by the
total weight to give a percentage retained on each sieve.
 The size of the average particles on each sieve then being analysis to get the cut point
or specific size range captured on screen.
 The results of this test are used to describe the properties of the aggregate and to see if
it is appropriate for various civil engineering purposes such as selecting the appropriate
aggregate for concrete mixes and asphalt mixes as well as sizing of water production
well screens.
 The results of this test are provided in graphical form to identify the type of gradation
of the aggregate.
A suitable sieve size for the aggregate should be selected and placed in order of decreasing
size, from top to bottom, in a mechanical sieve shaker. A pan should be placed underneath the
nest of sieves to collect the aggregate that passes through the smallest. The entire nest is then
agitated, and the material whose diameter is smaller than the mesh opening pass through the
sieves. After the aggregate reaches the pan, the amount of material retained in each sieve is
then weighed.
Preparation
In order to perform the test, a sample of the aggregate must be obtained from the source. To
prepare the sample, the aggregate should be mixed thoroughly and be reduced to a suitable size
for testing. The total weight of the sample is also required.
Reporting of results:
The results are presented in a graph of percent passing versus the sieve size. On the graph the
sieve size scale is logarithmic. To find the percent of aggregate passing through each sieve,
first find the percent retained in each sieve. To do so, the following equation is used,
%Retained = WSieve/WTotal ×100%
Where WSieve is the weight of aggregate in the sieve and WTotal is the total weight of the
aggregate. The next step is to find the cumulative percent of aggregate retained in each sieve.
To do so, add up the total amount of aggregate that is retained in each sieve and the amount in

30
the previous sieves. The cumulative percent passing of the aggregate is found by subtracting
the percent retained from 100%.
%Cumulative Passing = 100% - %Cumulative Retained.
The values are then plotted on a graph with cumulative percent passing on the y axis and
logarithmic sieve size on the x axis.
METHODS
There are different methods for carrying out sieve analysis, depending on the material
to be measured.
Throw-action sieving
Here a throwing motion acts on the sample. The vertical throwing motion is overlaid
with a slight circular motion which results in distribution of the sample amount over the whole
sieving surface. The particles are accelerated in the vertical direction (are thrown upwards). In
the air they carry out free rotations and interact with the openings in the mesh of the sieve when
they fall back. If the particles are smaller than the openings, they pass through the sieve. If they
are larger, they are thrown upwards again. The rotating motion while suspended increases the
probability that the particles present a different orientation to the mesh when they fall back
again, and thus might eventually pass through the mesh.
Modern sieve shakers work with an electro-magnetic drive which moves a spring-mass
system and transfers the resulting oscillation to the sieve stack. Amplitude and sieving time are
set digitally and are continuously observed by an integrated control-unit. Therefore sieving
results are reproducible and precise (an important precondition for a significant analysis).
Adjustment of parameters like amplitude and sieving time serves to optimize the sieving for
different types of material. This method is the most common in the laboratory sector.
Horizontal sieving
In a horizontal sieve shaker the sieve stack moves in horizontal circles in a plane.
Horizontal sieve shakers are preferably used for needle-shaped, flat, long or fibrous samples,
as their horizontal orientation means that only a few disoriented particles enter the mesh and
the sieve is not blocked so quickly. The large sieving area enables the sieving of large amounts
of sample, for example as encountered in the particle-size analysis of construction materials
and aggregates.
Tapping sieving
A horizontal circular motion overlies a vertical motion which is created by a tapping
impulse. These motional processes are characteristic of hand sieving and produce a higher
degree of sieving for denser particles (e.g. abrasives) than throw-action sieve shakers.

31
EXPERIMENT RESULTS:
For Coarse aggregate
Table 5.3 coarse aggregate test results
Sieve size Retained
(grams)
% Retained Cumulative (%) % finer
25 mm 0 0 0 0
20 mm 569 11.38 11.38 88.62
12.5 mm 3661 73.22 84.6 15.4
10 mm 619 12.38 96.98 3.02
4.75 130 2.6 99.58 0.42
Pan 21 0.42 100 0
RESULT: From Table 2, of IS 383 the sample is the single sized nominal aggregate
SPECIFIC GRAVITY TEST:
In Concrete technology, Specific gravity of aggregates is made use of in design
calculations of concrete mixes. With the specific gravity of each constituent known, its weight
can be converted into solid volume and hence a theoretical yield of concrete per unit volume
can be calculated.
Preparation of Test Sample
Coarse Aggregate
a) Sieve the test sample over the No. 4 (4.75 mm) sieve. The sample should be of sufficient
size to produce approximately 2100 grams of material retained on the No. 4 sieve. Discard the
material that passes this sieve.
b) Immerse the sample (plus No. 4 sieve size) in water for a period of not less than 15 hours.
c) After soaking, pour off the free water and allow the sample to come to a saturated surface
dry condition by spreading the sample on a flat, non-absorbent surface. The forced circulation
of air by means of a fan, if available, may hasten this process. The sample should be stirred
frequently to secure uniform drying. The predominance of free moisture may be removed
initially by rolling the sample back and forth in a clean, dry, absorbent cloth.
d) The sample may be considered to be saturated-surface-dry when the particles look
comparatively dull as the free moisture is removed from their surfaces. For highly absorptive

32
aggregates, the saturated-surface-dry condition is reached when there is an absence of free
moisture.
Test Procedure
 Weigh the saturated-surface-dry sample to the nearest 0.5-gram. For ease in
calculations, the fine aggregate sample may be brought to exactly 1000 grams weight,
and the coarse aggregate sample may be brought to exactly 2000 grams weight.
 Place the sample in the appropriate pycnometer containing approximately two inches
of water.
 Nearly fill the pycnometer jar with water at the same temperature plus or minus 3°F
(1.7°C) as used in the calibration.
 Screw the cap down into the proper position by lining up the mark on the pycnometer
top and the jar.
 Entirely fill the pycnometer by adding additional water through the hole in the
pycnometer top.
 Hold one finger over the hole in the top and gently roll and shake the pycnometer to
remove any trapped air in the sample.
When further rolling and shaking brings no more air bubbles to the top, fill, dry and weigh.
EXPERIMENT RESULT:
Saturated surface dry (SSD) sample weight (A) = 500.00 gm.
Pycnometer + water + SSD sample (B) =1847.00 gm.
Pycnometer + water (C) =1539.00 gm.
Oven dry Sample (D) =498.00 gm.
Specific gravity = 498/ [500- (1847-1539)]
= 498/192
= 2.5937

33
AGGREGATE IMPACT VALUE TEST:
This test is done to determine the aggregate impact value of coarse aggregates as per
IS: 2386 (Part IV) – 1963. The apparatus used for determining aggregate impact value of coarse
aggregates is Impact testing machine conforming to IS: 2386 (Part IV)- 1963,IS Sieves of sizes
– 12.5mm, 10mm and 2.36mm, A cylindrical metal measure of 75mm dia. and 50mm depth,
A tamping rod of 10mm circular cross section and 230mm length, rounded at one end and
Oven.
Preparation of Sample:
i) The test sample should conform to the following grading:
 Passing through 12.5mm IS Sieve – 100%
 Retention on 10mm IS Sieve – 100%
ii) The sample should be oven-dried for 4hrs. at a temperature of 100 to 110oC and cooled.
iii) The measure should be about one-third full with the prepared aggregates and tamped with
25 strokes of the tamping rod.
A further similar quantity of aggregates should be added and a further tamping of 25
strokes given. The measure should finally be filled to overflow, tamped 25 times and the
surplus aggregates struck off, using a tamping rod as a straight edge. The net weight of the
aggregates in the measure should be determined to the nearest gram (Weight ‘A’).
Procedure to determine Aggregate Impact Value:
i) The cup of the impact testing machine should be fixed firmly in position on the base of the
machine and the whole of the test sample placed in it and compacted by 25 strokes of the
tamping rod.
ii) The hammer should be raised to 380mm above the upper surface of the aggregates in the
cup and allowed to fall freely onto the aggregates. The test sample should be subjected to a
total of 15 such blows, each being delivered at an interval of not less than one second.
Reporting of Results:
i) The sample should be removed and sieved through a 2.36mm IS Sieve. The fraction passing
through should be weighed (Weight ‘B’). The fraction retained on the sieve should also be
weighed (Weight ‘C’) and if the total weight (B+C) is less than the initial weight (A) by more
than one gram, the result should be discarded and a fresh test done.
ii) The ratio of the weight of the fines formed to the total sample weight should be expressed
as a percentage.
Aggregate impact value = (B/A) x 100%

34
iii) Two such tests should be carried out and the mean of the results should be reported.
EXPERIMENT RESULT:
Table 5.4 aggregate impact value test results
Description Test 1 Test 2 Test 3
Weight of surface dry sample passing 12.5mm and retained on
10mm IS sieves,W1 (gm)
341 355 346
Weight of fraction passing on 2.36mm sieves after test,W2 (gm) 55 56.5 54
Weight of fraction retained on 2.36mm sieves after test,W3 (gm) 286 298 292
W4=W1-(W2+W3) (gm) 0 0.5 0
Aggregate Impact Value (A.I.V) = (W2/W1) * 100 (%) 16.13 15.92 15.61
Average Value A.I.V (%) 15.89
Note: If W4>1gm, discard and retest.
BULK DENSITY TEST:
Objective:
Calculating the bulk density of fine aggregate samples.
Bulk Density:
When dealing with aggregates it is important to know the voids that presents between
the aggregate particles, so that we decide whether to fill them with finer aggregate or with
cement paste. We all know that the Density we often deal with equals the mass divided by the
volume, when using this law to measure the density of aggregates the volume we use is the
volume of aggregate + the volume of the voids, and in this case we get a new quantity called
the Bulk Density. Bulk Density = Mass of the aggregate Volume of aggregate particles with
voids between them. This bulk density is used to convert quantities by mass to quantities by
volume. Bulk density depends on several factors: Size distribution of aggregates, Shape of
particles and degree of compaction. There are two methods this quantity is measured by
 Loose method.
 Compaction method.
Apparatus and Materials:
1. Container.

35
2. Glass Plate.
3. Fine and Coarse aggregate sample.
4. Water
5. Weighting Machine.
Procedure:
It is the same procedures for fine and coarse aggregate samples.
1. Weighing the empty container with the glass plate.
2. Fill the container with coarse aggregate to over flowing and then using the plate to level the
surface, and the weight of the container and the plate and the coarse sample is found. (W1)
3. Empty the container from the coarse aggregate and refill it with the fine aggregate to over
flowing and then level the surface using the plate, and the weight of the container and the plate
and the fine sample is found. (W2)
4. Empty the container again and this time we fill it with water till the rim of it and place the
plate on it, no water bubbles should present on the surface, and we weight the container and
the plate and the water. (W3)
EXPERIMENT RESULT:
DRY LOOSE BULK DENSITY TEST:
Coarse aggregate – 20mm
Dry loose bulk density = 1366.67 gm / lit

36
DRY COMPACTED BULK DENSITY TEST:
WATER ABSORPTION TEST:
This test helps to determine the water absorption of coarse aggregates as per IS: 2386
(Part III) – 1963. For this test a sample not less than 2000g should be used. The apparatus used
for this test are:
 Wire basket, perforated, electroplated or plastic coated with wire hangers for
suspending it from the balance
 Water-tight container for suspending the basket
 Dry soft absorbent cloth – 75cm x 45cm (2 nos.)
 Shallow tray of minimum 650 sq.cm area
 Air-tight container of a capacity similar to the basket and Oven.
Procedure to determine water absorption of Aggregates.
i) The sample should be thoroughly washed to remove finer particles and dust, drained and
then placed in the wire basket and immersed in distilled water at a temperature between 22 and
32C.
ii) After immersion, the entrapped air should be removed by lifting the basket and allowing it
to drop 25 times in 25 seconds. The basket and sample should remain immersed for a period
of 24 + ½ hrs afterwards.

37
iii) The basket and aggregates should then be removed from the water, allowed to drain for a
few minutes, after which the aggregates should be gently emptied from the basket on to one of
the dry clothes and gently surface-dried with the cloth, transferring it to a second dry cloth
when the first would remove no further moisture. The aggregates should be spread on the
second cloth and exposed to the atmosphere away from direct sunlight till it appears to be
completely surface-dry. The aggregates should be weighed (Weight ‘A’).
iv) The aggregates should then be placed in an oven at a temperature of 100 to 110oC for 24hrs.
It should then be removed from the oven, cooled and weighed (Weight ‘B’).
Formula used is Water absorption = [(A - B)/B] x 100%.
Two such tests should be done and the individual and mean results should be reported.
EXPERIMENT RESULT:
Coarse aggregate – 20mm:
Weight of Saturated Surface Dry (SSD) sample (A) =705.00 gm.
Weight of Oven dry Sample (B) =703.00 gm.
Weight Absorption = 705-703/703X 100
= 0.00284X 100
= 0.28 %
Coarse aggregate – 10mm:
Weight of Saturated Surface Dry (SSD) sample (A) = 653.50 gm.
Weight of Oven dry Sample (B) = 650.00 gm.
Weight Absorption = 653.5-650/650X 100
= 0.00538X 100
= 0.54 %

38
FLAKINESS INDEX TEST:
Flakiness Index is the percentage by weight of particles in it, whose least dimension
(thickness) is less than three-fifths of its mean dimension. The test is not applicable to particles
smaller than 6.3 mm in size.
Procedure for using Gauge for Flakiness Index
A balance of suitable capacity, gauge for Flakiness Index and a set of Sieves of relevant
sizes as per the specified Standard will be required.
Sample size will be such that at least 200 pieces of any fraction to be tested will become
available. The aggregates will be dried to a constant weight in an oven at a temperature of 110º
± 5ºC and weighed to the nearest 0.1g. The aggregates will then be sieved through the set of
prescribed sieves.
Each fraction is then gauged for thickness through the slots of the gauge. All the pieces
passing through the gauge are collected and weighed to an accuracy of 0.1 percent of the weight
of the sample.
The Flakiness Index is the total weight of the material passing various gauges and sieves
expressed as a percentage of the total weight of the sample gauged.
EXPERIMENT RESULT:
Table 5.5 flakiness index
Passing through
IS Sieve
Retained on
IS Sieve
Weight Of The
Sample Retained
Weight Of The
Sample Passed
Total Weight Of
The Sample
40 25 0 0 0
25 20 1947 361 2308
20 16 1278 246 1524
16 12.5 501 276 777
12.5 10 281 75 356
10 6.3 104 41 145
Σ=999 Σ=5110
Flakiness index = 999/5110 X 100
= 0.1955 X 100
= 19.55 %

39
ELONGATION INDEX TEST:
The elongation index on an aggregate is the percentage by weight of particles whose
greatest dimension (length) is greater than 1.8 times their mean dimension. The elongation
index is not applicable to sizes smaller than 6.3 mm.
The test is conducted by using metal length guage of the description. A sufficient
quantity of aggregate is taken to provide a minimum number of 200 pieces of any fraction to
be tested. Each fraction shall be guaged individually of length ion the metal gauge. The total
amount retained by the gauge length shall be weighed to an accuracy of at least 0.1 per cent of
weight of the test sample taken. The elongation index is the total weight of the material retained
on the various length gauges expressed as a percentage of the total weight of the sample gauged.
The presence of elongated particles in excess of 10 – 15 per cent is generally considered
undesirable, but no recognized limits are laid down.
Indian standard explain only the method of calculating both flakiness index and elongation
index. But the specification does not specify the limits. British standards BS 882 of 1992 limits
the flakiness index of the coarse aggregate to 50 for natural gravel and to 40 for crushed coarse
aggregate. However, for wearing surfaces a lower value of flakiness index are required.
EXPERIMENT RESULT:
Table 5.6 elongation index test result
Passing through
IS Sieve
Retained on
IS Sieve
Weight Of The
Sample
Retained
Weight Of The
Sample Passed
Total Weight Of
The Sample
40 25 0 0 0
25 20 38 2270 2308
20 16 81 1443 1524
16 12.5 129 648 777
12.5 10 64 292 356
10 6.3 45 100 145
Σ= 357 Σ=5110
Elongation index =357/5110 X 100
= 0.06986 X 100
= 6.98 %

40
5.3 TESTS ON FRESH CONCRETE:
SLUMP TEST:
After the fresh concrete is prepared Slump test is done. Slump test is the most
commonly used method of measuring workability of concrete which can be employed either in
laboratory or at site of work. It is not a suitable method for very wet or very dry concrete .It
does not measure all factors contributing to workability, nor is it always representative of the
placability of the concrete.
The apparatus for conducting the slump test essentially consists of a metallic mould in the form
of a frustum of a cone having the internal dimensions as under:
 Bottom diameter: 20 cm
 Top diameter: 10 cm
 Height: 30 cm
The mould is then filled in four layers, each approximately l/4 of the height of the mould.
Each layer is tamped 25 times by the tamping rod taking care to distribute the strokes evenly
over the cross section.
After the top layer has been rodded, the concrete is struck off Level with a trowel and
tamping rod. The mould is removed from the concrete immediately by raising it slowly and
carefully in a vertical direction.
This allows the concrete to subside. This subsidence is referred as SLUMP of concrete.
The difference in level between the height of the mould and that of the highest point of the
subsided concrete is measured. This difference in height in mm is taken as Slump of Concrete.

41
 If the concrete slumps evenly it is called true slump. If one half of the cone slides down,
it is called Shear slump. In case of a shear slump, the slump value is measured as the
difference in height between the height of the mould and the average value of the
subsidence. Shear slump also indicates that the concrete is non-cohesive and shows the
characteristic of segregation.
5.4 TESTS ON WATER:
 pH Value
 Chloride
 Sulphite
 Nitrite
5.5 TESTS ON HARDENED CONCRETE:
 Compressive Strength
 Flexure Strength

42
CHAPTER 6
MIX DESIGN PROCEDURE
The procedure for designing concrete mix as per new code is highlighted using an M20
concrete.
Design stipulations for proportioning
 Grade designation: M50
 Type of cement: OPC 53 grade, IS 8112
 Max. Nominal size of aggregate. : 20 mm
 Minimum cement content: 350 kg/m3
 Maximum water cement ratio: 0.45
 Exposure condition: Extreme
 Degree of supervision: Very Good
 Type of aggregate: Crushed angular aggregate
 Maximum cement content: 480 kg/m3
 Chemical admixture: Glenium, BASF
Test data for materials
 Cement used: OPC 53 grade
 Specific gravity of cement : 3.15
 Specific gravity of
a. Coarse aggregate: 2.60
b. Fine aggregate: 2.59
 Water absorption
a. Coarse aggregate: 0.28 %
b. Fine aggregate: 0.59 %
 Free (surface) moisture
a. Coarse aggregate: Nil
b. Fine aggregate: 2.0 % 57
 Sieve analysis
a. Coarse aggregate: Conforming to Table 2 of IS 383

43
Table 6.1: sieve analysis results
Sieve size Retained
(grams)
% Retained Cumulative (%) % finer
25 mm 0 0 0 0
20 mm 569 11.38 11.38 88.62
12.5 mm 3661 73.22 84.6 15.4
10 mm 619 12.38 96.98 3.02
4.75 130 2.6 99.58 0.42
Pan 21 0.42 100 0
b. Fine aggregate: Conforming to Zone II of IS 383
Table 6.2 fine aggregate test results
Sieve
size
Weight
(gm)
Retained
%
(col.2/W)
Cumulative
%
% of
Passing
(100 –
col.4)
Specification limits as
per Table-2 as per
IS383
1 2 3 4 5 Zone-
1
Zone-
2
Zone-
3
10.00mm 0 0 0 100 100 100 100
4.75mm 15.9 1.59 1.59 98.41 90-
100
90-100 90-100
2.36mm 128.4 12.84 14.43 85.57 60-95 75-100 85-100
1.18mm 102.5 10.25 24.68 75.32 30-70 55-90 75-100
0.600mm 321.3 32.13 56.81 43.19 15-34 35-59 60-79
0.300mm 213.5 21.35 78.16 21.84 5-20 8-30 12-40
0.150mm 91.2 9.12 87.28 12.72 0-10 for River sand & 0-
20 for Crusher sand
0.075mm 48.1 4.81 92.09 7.91 0-8 for River sand & 0-15
for Crusher sand

46
Table 6.3 Approximate Air Content
Nominal maximum
Size of coarse aggregate (mm)
Entrapped air
(% of volume of concrete)
40 1.0
20 2.0
10 3.0
Table 6.4 Suggested Values of Standard Deviation
Grade of concrete Standard deviation for different degree of control
(N/mm2)
Very good Good Fair
M10 2.0 2.3 3.3
M15 2.5 3.5 4.5
M20 3.6 4.6 5.6
M25 4.3 5.3 6.3
M30 5.0 6.0 7.0
M35 5.3 6.3 7.3
M40 5.6 6.6 7.6
M45 6.0 7.0 8.0
M50 6.4 7.4 8.4
M55 6.7 7.7 8.8
M60 6.8 7.8 8.8

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MINIMUM CEMENT CONTENT & MAX. WATER CEMENT RATIO
REQUIRED IN CEMENT CONCRETE TO ENSURE DURABILITY UNDER
SPECIFIED CONDITIONS OF EXPOSURES
Table 6.5
(Extract of para 5.4.3 & 5.4.5 of IRS Concrete Bridge Code)
Exposure R.C. Concrete Prestressed Concrete
Minimum
cement
content
Maximum
water
cement
ratio
Minimum
cement
content
Maximum
water
cement
ratio
Mild 350 0.45 400 0.40
Moderate 400 0.40 400 0.40
Severe 400 0.40 430 0.40
Very Severe 430 0.38 440 0.35
Extreme 430 0.35 440 0.35
Table 6.6 DEGREE OF QUALITY CONTROL EXPECTED UNDER DIFFERENT
SITE
CONDITIONS
Degree of
Control
Conditions of Production
Very Good Fresh cement from single source and regular tests, weigh batching of all
materials, aggregates supplied in single sizes, control of aggregate
grading and moisture content, control of water added, frequent
supervision, regular workability and strength tests, and field laboratory
facilities.
Good Carefully stored cement and periodic tests, weigh batching of all
materials, controlled water, graded aggregate supplied, occasional
grading and moisture tests, periodic check of workability & strength,
intermittent supervision, and experienced workers.
Fair Proper storage of cement, volume batching of all aggregates, allowing
for bulking of sand, weigh-batching of cement, water content controlled
and occasional supervision and tests.

48
Table 6.7 APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METER
OF
CONCRETE
(Applicable for concrete upto grade M 35)
Zone II Sand, W/C Ratio = 0.60, Workability = 0. 80 C.F
Maximum size of
aggregate
(mm)
Water content including
surface water, per cubic
meter of concrete
( Kg)
Sand as percent of total
aggregate by absolute
volume
10 208 40
20 186 35
40 165 30
Table 6.8 APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METER
OF
CONCRETE
(Applicable for concrete above grade M 35)
Zone II Sand, W/C Ratio = 0.35, Workability = 0. 80 C.F
Maximum size of
aggregate
(mm)
Water content including
surface water, per cubic
meter of concrete
( Kg)
Sand as percent of total
aggregate by absolute
volume
10 200 28
20 180 25
Table 6.9 ADJUSTMENT OF VALUES IN WATER CONTENT AND SAND
PERCENTAGE FOR OTHER CONDITIONS
Change in conditions stipulated for tables Adjustment required in
Water content % sand in total
aggregate
For sand conforming to grading Zone I,
Zone-III or Zone IV of Table-4, IS: 383-
1970
0 + 1.5 for Zone I
- 1.5 for Zone III
- 3.0 for Zone IV
Increase or decrease in the value of
compacting factor by 0.1
+3% 0
Each 0.05 increase or decrease in water-
cement ratio
0 +1%
For rounded aggregate - 15 kg/m3 - 7%

49
Target mean strength for mix proportioning
fm= fck +1.65*standard deviation
From Table 1 of IS 10262:2009 standard deviation, s = 6.4 N/mm2
(For very good control)
Therefore target strength = 50+1.65 x6.4 = 60.56 N/mm2
Selection of w/ c ratio
 Water - cement ratio (from Fig. 2) = 0.35 (using data from above).
 Maximum water - cement ratio specified for durability condition = 0.45 (from
Table-6.5).
 Water cement ratio to be adopted for concrete = 0.45 (Lower of 4.5).
 Water content from Table -6.8 = 180 (for a workability of 0.80 C F).
 Sand as percentage of total aggregate by absolute volume from Table-6.8 = 25%
For W/C ratio of 0.35.
 Adjustment of water content (using table-6.9)
(For C F of 0.90) = 180 + .03 x 180 = 185.4 kg/m3.
 Adjustment for sand content (using Table -6.9)
25% - 3.0% = 22% (for W/C of 0.45)
 Modified water content = 185.4 liters
 Modified sand content = 22%
 Cement content = 185.4/0.45=412 kg/m3
 Minimum Cement content = 350 kg/m3 (from Table-6.5 specified for durability
Condition).
 Required Cement content = 412 kg/m3 (Higher of above value).
 Entrapped air, as percentage of volume of concrete = 2%.
 From Table 5 of IS 456, minimum cement content for Extreme exposure condition =
360 kg/m3, Hence ok.

50
DETERMINATION OF COARSE AND FINE AGGREGATE CONTENT:
V= [W + C/SC + 1/P*Fagg/SFine] x 1/1000
V= [W + C/SC + 1/ (1-P)*Cagg/SCoarse] x 1/1000
V = absolute volume of fresh concrete
Sc =specific gravity of cement.
W= mass of water (kg) per m3 of concrete
C= mass of cement (kg) per cu.m. Of concrete.
p = ratio of fine aggregate to total aggregate by absolute volume.
Fa, Ca= total masses of fine and coarse aggregates by absolute volume.
Sfa, Sca= specific gravities of fine and coarse aggregates (saturated surface dry condition).
For the Specified Max. Size of aggregate of 20 mm, the amount of entrapped air in the
wet concrete is 2%.
Amount of Fine aggregate, Fa required
1 m3 = [185.4 + 412/3.15 + 1/0.315* Fagg/2.59] x 1/1000
Fa =630 kg/m3.
Amount of Coarse aggregate, Ca required
1 m3 = [185.4 + 412/3.15 + 1/ (1-0.315)* Cagg/2.60] x 1/1000
Ca = 1377 kg/m3.
The Mix Proportion then becomes
 Water = 185.4 kg/m3
 Cement = 412 Kg/m3
 Fine Aggregate = 630 Kg/m3
 Coarse Aggregate = 1377 Kg/m3
Mix proportions for making 1 cu.m of concrete:
Table 6. material contents in M 50:
Water Cement Fine Aggregate Coarse Aggregate
185.4 kg/m3 412 Kg/m3 630 Kg/m3 1377 Kg/m3

51
CHAPTER 7
MERITS AND DEMERITS
7.1 MERITS OF RMC:
 Better quality concrete is produced.
 Elimination of storage space for basic materials at site.
 Elimination of Procurement / Hiring of plant and machinery.
 Wastage of basic materials is avoided.
 Labour associated with production of concrete is eliminated.
 Time required is greatly reduced.
 Noise and dust pollution at site is reduced.
 Organization at site is more streamlined.
 Durable & Affordable
 No storage space required either for raw materials or for the mix.
 Lower labour and supervisory cost.
 No wastage at site.
 Environment friendly.
 Availability of concrete of any grade.
7.2 DEMERITS OF RMC:
 Need huge initial investment.
 Not affordable for small projects (small quantity of concrete)
 Needs effective transportation system from R.M.C to site.
 Traffic jam or failure of vehicle creates problem if proper dose of retarder is not given.
Labours should be ready on site to cast the concrete in position to vibrate it and compact it.

52
CHAPTER 8
OPERATIONAL ASPECT
8.1 NEEDS TO BE SPECIFIED BY CONSUMER FOR RMC
The following needs to be specified very clearly:
 Characteristic strength or grade (N/mm2)
 Target workability or slump in mm required at site
 Exposure conditions for durability requirements
 Maximum water to cement ratio
 Minimum cement content
 Maximum aggregate size
 Type of cement
 Mineral admixture and its proportion (Kg/m3)
 Maximum aggregate size
 Rate of gain of strength (for formwork removal or prestressing etc.)
 Maximum temperature of concrete at the time of placing (in extreme climatic
conditions or in case of massive concrete pours)
 Type of surface finish desired.
 Method of placing
 Rate of supply desired to match the placing and compaction speed planned at site.
 Quantity of concrete required.
 Lift and lead of concrete transportation and placement at site.
 Frequency of concrete testing
 Details of materials and their required tests.
 Permeability tests required (if any)
 Placing of concrete in formwork to be under scope of RMC supplier (if required)
 Permissible wastage
 Mode of measurement.

53
8.2 INFORMATION TO BE SUPPLIED BY THE PRODUCER
The RMC supplier must provide the following information to the consumer if and when
requested:
 Nature and source of each constituent material including the name of the manufacturer
in case of branded products like cement, admixtures etc.
 Proportion of quantity of each constituent per CuM of fresh concrete.
 Generic type of the active constituent of the chemical admixture and its solid content.
 Chloride content in all constituent materials.
 Compatibility of cement and chemical/mineral admixtures.
 Compatibility of admixtures with one another when more than two types of admixtures
are proposed.
 Initial and final setting time of concrete when admixture is used.
 Details of plant and machinery (capacity CuM/hr), storage (CuM) availability, type of
facilities to dose admixtures, type of moisture measurement arrangement, type of mixer,
rated capacity (CuM/min.) of the mixer.
 Availability of number of transit mixers and their capacities.
 Details of last calibrations done on various weighing /dosing equipments.
 Testing facilities available at RMC plant.
 Capacity and type of concrete pump and placing equipment available (if required).
8.3 CHECKS BY CONSUMER BEFORE ORDERING THE RMC
The following need to be looked into by the consumer:
 Reliability of the plant and transit mixers for consistent and continuous concrete supply
as per requirement.
 Calibrations of all measuring devices and their accuracy.
 Mode of operation of plant should preferably be fully automatic and not manual.
 Quality of materials proposed to be used.
 Adequacy of quantity of materials proposed to be used.
 Compliance of concrete specifications based on the mix parameters specified.

54
 Adequacy of testing facilities.
 Time likely to be taken by transit mixers from plant to site and back.
8.4 CHECKS NEEDED AT SITE PRIOR TO RECEIPT OF RMC
 Reinforcement layout for proper concrete placement without segregation.
 Adequacy of formwork to take the hydrostatic pressure and adequacy of loading on
propping system to match the speed of placing.
 Openings and chutes provided, at predetermined locations, between reinforcement bars
to lower the placing hose (if pumped concrete is planned) to avoid segregation of
concrete.
 Adequacy of manpower and equipment for placing, compacting, finishing and curing
of concrete.
 Proper approach for transit mixers free from all encumbrances ego water logging,
material stacking etc.
 Proper platform to receive concrete.
 Proper precautions required to be taken to ensure that concrete from the transit mixer is
unloaded at the fastest possible speed does not take more than 30 minutes.
 If pumping is proposed, the location of the pump should be approachable from both
sides.
8.5CHECKS NEEDED AT SITE DURING CONCRETING:
 Proper co-ordination between the RMC supply and placing and compacting gangs.
 Proper signaling or communication at site is necessary.
 Workability of concrete within accepted limits.
 Adequacy of cohesiveness of concrete for pumpability.
 Ensure that water addition or chemical admixtures are not added during transportation
by RMC unauthorized persons and without the knowledge of the site in charge of the
consumer.
 Temperature of concrete at the time of receipt at site (if specified).

55
 Continuous and steady supply at site and speedy unloading of the Monitor speed and
progress of placing to avoid formation of cold joints transit mixers.
 Monitor proper placement without segregation.
 Monitor placement of concrete at the closest possible point to its final location.
 Arrange for curing as soon as finishing is completed. This is specially required in case
of slabs, pathways and roads in hot/warm weather.
 Retempering should be prohibited as experiments shows the addition of water to RMC
truck at the construction site may result in substantial reduction in strength. The
reduction in strength was found to be proportional to the increase in slump. Large
increase in slump means higher reduction in strength. When the amount of water added
is not controlled, reduction of strength may be as high as 35%. In cases where controlled
amount of water is added to restore the slump within the specification’s limits (100 ±25
mm), the reduction of strength may be below 10%.
8.6 THE UNNECESSARY RESTRICTIONS ON SUPPLIERS OF RMC BY
PURCHASER
 Insistence on use of cement and admixtures of specific brands: This selection should be
left to the RMC supplier as they have to decide this based on the comparability study.
 Inappropriately low water to cement ratio. This should be left to the RMC supplier or
alternatively high strength of concrete specified.
 Restriction on use of water reducing admixtures. It is almost mandatory to use water
reducing and or slump retaining admixtures. Hence such restrictions can cause quality
problems.
 Insisting on Indian Standard method of concrete mix design: It must be understood that
IS 10262 (1982) only gives guidelines on design of concrete mixes. It does not cover
high strength cements now available and does not cater to effects of admixtures. It also
does not recommend changes necessary for RMC and pumpable concrete mixes.
Concrete mixes designed by this method are generally found to be non-cohesive and
require higher cement contents (uneconomical). The option of concrete mix design
should be and must be left to the RMC supplier.
 Frequency of testing: This is often changed by the consumer than that specified in
clause 6.3.2 of IS 4926 (2003). However, this needs to be mutually discussed and
finalised prior to placement of order.
 Fixed slump insisted upon: Many a times fixed slump value is insisted upon by the
consumer. This is practically not possible. Variations are likely to occur and should be
within the limits say ± 25 mm as stated in clause 6.2.1 of IS 4926 (2003).

56
 Ambiguous specifications: Many consumers give ambiguous specifications. Both the
specifier and the supplier need to resolve the ambiguity specially those dealing with
specifications like durability as per IS 456 (2000) without mentioning exposure
conditions or presence of chemicals in ground water and subsoil. Also specifying target
mean strength instead of characteristic strength required without mentioning the
accepted failure rate or standard deviation.
 Concrete Field strength should not be less than Target strength: Such a specification
that the field strength should not be less than the target strength should not be less than
the target strength belies the understanding of the definition of characteristics strength.
If the requirement is for an M30 grade concrete, then the field strength of concrete
should not be less 30 N/mm2 within a confidence limit of 95%. If the specification
insists on target strength to be achieved in the field as well, then the concrete requested
automatically becomes M39 or its equivalent. This makes the concrete unnecessarily
expensive.
8.7 THE CONSTRAINTS FACED BY RMC PRODUCERS AT PRESENT
 RMC cost is likely to be slightly higher than site produced concrete of the same quality.
This may be mainly due to sales taxes. However, to some extent if RMC consumer has
no objection to addition of flyash or ground granulated blast furnace slag of required
quality and consistency then perhaps the cost becomes more competitive with site
produced concrete. RMC plants having accurate computerised batching and excellent
mixing facilities can produce good quality RMC if they are careful in selecting the
mineral admixture.
 Delayed payments and long credit period insisted upon by consumers affect their cash
flow.
 RMC plants in cities are not permitted to be installed in residential zones. This results
in their installation nearly 10-20 kms. Away from their potential consumers located in
residential zones.
 High cost of the plant and equipment results in high capital costs. However, many
multinationals have started producing plant and equipment in our country. Hence costs
have reduced. However, one has to be careful as quality of performance has dropped in
comparison with equipment directly imported from countries like Germany.
 Bad quality of roads and traffic congestion and intermittent signals often delay the
deliveries in metros.
 Availability of trained and skilled manpower for operations and maintenance of plant
and equipment. As new plants come up, skilled workers keep changing jobs for better
prospects.
 Price variations of all concrete ingredients specially cement.

57
 Non availability of consistent and good quality aggregates, mineral admixtures etc.
 Non-availability of bulk cement supply in most of the cities where RMC is marketed.
 Difficulty in immediate availability of spares or additional inventory carrying cost
required to be kept in case of essential spares.
 Stipulations of pollution control board causing difficulty to obtain license for running
RMC plant. Such clearances are not required if similar plants are installed on the
construction site itself.
 Workability retention in hot weather.
Site oriented problems at the consumer end such as the following:
 Delays in placing, compacting and finishing at consumer's end causes delays in
unloading of transit mixer and stiffening of the concrete mix.
 Quality of formwork and its adequacy to take proper vertical loads and hydrostatic
pressures, due to faster rate of supply and placing is often not taken care of at sites
receiving concrete.
 Reinforcement layout and planning of placement, compaction and curing must be
properly organised at site to suit the speed of supply and placement of RMC.
 In many countries, specialist agencies do pumping and placing of concrete. In our
country, the onus of pumping and placing is either placed on the RMC supplier or on
the construction site.
 Concrete cube failures and their acceptance criteria due to site inadequacies or
sampling should not be attributed to RMC supplier.
 Plastic shrinkage cracks due to inadequate curing at site often results in blaming the
RMC supplier.

58
CHAPTER 9
CONCLUSION
The concrete quality produced in RMC plant is highly consistent with low deviation
order. It provides a high degree of overall strength of hardened concrete and the performance
of the structure at a later date. RMC operations are highly mechanized and fully controlled
through electronic controls and hence reduce the probability of errors in various operations. It
is also environment friendly and brings down pollution due to dust at construction can also be
accelerate with the use of RMC. The use RMC in civil construction is widely adopted
throughout the world. The beginning made in India is in tune with the developments outside
and RMC uses provide numerous benefits to the consumers.
Conventional approach to durable concrete structures, namely specifying maximum
water cement ratio, minimum cement content and cement type, is now always satisfactory,
especially under aggressive environmental condition. Site manufactured concrete cannot assure
the same quality of concrete and that from controlled ready mix batching plant backed by
advanced technology and project management. The advantages of RMC are particularly
evident in construction projects with aggressive exposure conditions.
Ready mix concrete has gained acceptance in Indian industry due to several advantages
including quality control and overall economy. RMC plants are proliferating, especially in
urban regions, not only because of the space restrictions around construction site but also due
to the realisation of the advantages by engineers and construction industry.

59
CHAPTER 10
REFERENCES
 Concrete Technology Theory and Practice, M.S SHETTY, S.Chand- New Delhi.
 “RMC in India” (June 2001), Civil Engineering & Construction Review
 IS 4926-2003, Standard on Ready mixed concrete – Code of Practice, BIS, New
Delhi.
 IS 383, Indian Standard specification for coarse and fine aggregates from natural
sources for concrete (Second Revision)
 IS 10262-2009, Indian Standard Concrete Mix Proportioning- guidelines (First
Revision)
 IS 456-2000, Indian Standard Plain and Reinforced Concrete - Code of Practice
(Fourth Revision)
 “RMC on the move” (Oct. 2003), Ambuja Technical Literature, Vol. No. 90
 “Mechanisations of concreting, Part I- Batching, Mixing & Transporting” (Dec.
1996), Ambuja Technical Literature, Vol. No. 12
WEBSITES:
 http://www.jklakshmi.com/calculator.html
 http://www.lntecc.com/concrete/lntreadymix.asp
 http://www.rdcconcrete.com/
 http://www.scribd.com/
 http://www.wikipedia.org/

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